Editor’s note: This post has been updated to note the nature of Shields’s discharge from the military.

NEW CARROLLTON, Md. – Theran Shields once defended the country. Now he guards the coffee warehouse.

The job site is tucked off a winding road on a secluded side of New Carrollton, near a rubber equipment store and an shoe repair shop. Nearby is a bus stop where no one appears to wait for the bus, and a small patch of a forest filled with skinny trees.

“Expect the unexpected,” Shields’s supervisor, Edwin Reyes, told him.

“That’s right, I’m looking out for anything,” Shields responded.

Suddenly, the metal fence behind them started to rattle. They both turned their heads swiftly. Someone was trying to get through the gate.

Turned out to be a balding worker wearing a hairnet. He tried to open the fence, but it appeared jammed.

Shields ran into his small station near the parking lot, and pushed a button. Problem solved.

America’s preoccupation with safety and struggle with high-profile shootings has resulted in a boom in the number of security guards and private patrol officers. More than 680,000 work in the field, federal labor statistics show, a 20 percent increase since 2004. The security industry has grown four times faster than the private-sector labor market over that period.

The first spike came after 9/11, according to Michigan State University criminal justice professor Mahesh Nalla. Back then, companies all along the private sector redid security plans to prepare for unlikely tragedies. The security field became a $7 billion industry.

Those numbers began to slow down during the recession, but picked up again after a barrage of shootings in highly populated areas that don’t involve gangs or drugs violence, a category the FBI calls “active shootings.” Those shootings include events that the country can identify by a single name alone: Aurora. Newtown. Navy Yard.

The FBI recently released a report looked at active shootings over the past 14 years, and discovered between the first and second half of the study. The seven years averaged 6.4 incidents annually, the last seven years averaged 16.4. The result is a country in which private security personnel outnumber police officers three to one.

Out of this boom came Shields’s employer, Blueline Security Services. Shawn Scarlata founded the company with three other longtime Prince George’s County police officers in 2008, eager to capitalize on the increased desire for security within the nation’s capital. In six years, they’ve grown from one employee to 280.

Now he receives at least 100 job applications a week. The lure for greater security is also matched by the desires of residents seeking working-class jobs. The crush of applications allow him to be selective – all of his security guards have prior experience, or a college education, or have served in the military.

Still, the jobs are not nearly as dangerous as those held by loggers or fishermen. The truth is, for any life-threatening occurrence that a security guard might prevent, there can be hundreds of thousands of hours in tedium.

For three weeks, Shields has guarded the entrance of the distribution center for Eight O’Clock Coffee. He scans the place for suspicious people. He keeps his ears attuned for any unusual noises. He sniffs hard for any distinct aromas, aside from the coffee, because this is an unpredictable world and who knows where trouble might lurk.

Usually, though, he just lets cars in and out of the parking lot.

It’s the balance between the boring and the potential of perilous that can make the job a challenge, and a blip in concentration can lead to embarrassing, dangerous blunders.

“So the trick is to stay alert,” Shields said.

It’s a trick Shields, 29, learned during eight years in the military, as an airborne sniper in Afghanistan, working on tactical missions, guarding nuclear weapons facilities in the United States. Shields says he is currently appealing a bad conduct discharge. He pleaded guilty to misdemeanor larceny charges after a theft at a Wal-Mart when he was in the military, times he’d like to forget.

As a civilian, he wanted to make his living through a home remodeling business. That idea hasn’t fully taken off, and he is a single father of a 7-year-old, so he sought out security work. The veteran was trained to use pepper spray and small handcuffs. He was given a small baton that fits just right in his duty belt.

“Relaxing,” is how Shields described his new job. Except that he can’t really relax. Reyes, the supervisor, drilled him with scenarios that might happen. “What if someone jumps the fence?” “What if some car crashes through?” “What if you see someone drive in, looking around suspiciously?” “What if someone rushes from the bus stop?”

“What if I stop asking these questions?” Shields said. “That’s how you have what happened to the Secret Service. That’s how you have people jumping the White House fence.”

The Secret Service has faced increasing scrutiny after a knife-wielding man jumped over the White House fence, an incident that ultimately led to the resignation of Secret Service Director Julia Pierson.

There are other tricks to keep security guards alert. Some places have check points throughout the facility, where security guards check in every 15 minutes. Some cruisers set off an alert to the management office if they stayed in the same place too long. From the outside, it might seem as if it’s all an exercise in fear-mongering. But those questions seem irrelevant if – when? – a tragedy were to occur.

“Other [places where I work security] are a little more active,” Shields said. “I sometimes walk through an apartment complex where there were a lot of domestic disputes. Two months ago, there was a dead body.”

Everyone’s alive at the warehouse, but the place seemed a little dead. A good thing, Shields added.

The trucks barrel into the entryway, but they were expected to make deliveries, according to Shields’s logbook. The trees bristled; but it was just the wind. The bus sped by but dropped no one off. More people in hairnets stepped out to catch some fresh air, and a caravan came to the site with a driver who looked around, but realized they were in the wrong spot, and made a U-turn. Then, nothing happened.

It was noon – and two hours of nothingness, or chaos, awaited him. His eyes fixed on the parking lot, the trees, the facility. So far, everything seemed safe. Just as it had been for the past three weeks.